1. Field of the Invention
This invention relates to force balancing weighing systems, and more particularly to such systems useful in machines for packaging fluidized dry, divided, solid material into containers such as paper bags, for example.
2. Description of the Prior Art
Packaging machines of the class described are well known to those skilled in the art, and are exemplified in U.S. Pat. No. 3,261,379 which discloses apparatus including a bin for fluidizing the material to be packaged and a tubular element or conduit for conducting such fluidized material to a filling spout which may constitute the discharge end of the conduit and upon which a bag may be secured to receive a charge of the material. The bag may be weighed and the flow of material cut-off when a predetermined weight is reached, cut-off being effected by pinching a flexible tube forming a portion of the conduit through which the fluidized material moves from the bin to the filling spout.
As further shown in U.S. Pat. No. 3,261,379, it is known in the art to mount the filling spout and a bag clamp on a bag support frame including a pair of legs suspended from a scale beam by knife edge fulcrums. The beam includes rearwardly extending members that are in turn supported on knife edge fulcrums mounted on a main frame which is separate from the frame mentioned above, and the rear portion of the beam supports a weight basket through knife edge fulcrums.
The bag support frame includes a bag seat for supporting bags to be filled and weighed and means are provided to discharge the bags from the seat.
While packaging apparatus of the class described that use weighing mechanisms of the scale beam type have achieved a degree of commercial success, nevertheless bag filling was not effected with the precision desired in the art due in part to imbalances in the knife edge fulcrums, but primarily due to the effect of incidental forces on the scale caused by random placement of the bag on the bag seat. Thus, for example, such incidental forces were often caused in the filling of a bag, which was laterally offset with respect to the vertical centerline of the weighing apparatus, these forces leading to cut-off of the flow of material at other than the desired filled bag weight.
Since commercialization of the structure disclosed in U.S. Pat. No. 3,261,379, the use of a load cell-microcomputer combination has been developed as part of the weighing system. Thus, a microcomputer responds to a load cell accurately to weigh, monitor, checkweigh and display bag weights. However, the full potential of these functions inherent in the load cell-computer conbination could not be realized with the conventional weighing system because of the incidental forces mentioned above.